The present invention relates to an ultrasound diagnostic apparatus suitable for measuring an elastic modulus of a vascular wall. In particular, the present invention relates to an ultrasound diagnostic apparatus capable of displaying an M-mode image of a heartbeat suitable for measuring an elastic modulus of a vascular wall in good condition.
Ultrasound diagnostic apparatuses using ultrasound images are put to practical use in the medical field.
In general, this type of ultrasound diagnostic apparatus has an ultrasound probe (hereinafter referred to as a probe) and a diagnostic apparatus body. The ultrasound diagnostic apparatus transmits ultrasonic waves from the probe into a subject's body, receives an ultrasonic echo from the subject's body with the probe, and electrically processes the resulting reception signals in the diagnostic apparatus body to produce an ultrasound image.
Also, ultrasonic waves are transmitted toward a blood vessel, a cardiac wall, or the like, an ultrasonic echo therefrom is received, a reception signal is analyzed to obtain an amount of displacement of a vascular wall or the like, and based on the displacement amount, the elastic modulus of the vascular wall, the cardiac wall (heart muscle) or the like is measured.
For example, JP 10-5226 A describes that ultrasonic waves are transmitted and received to and from an object moving in synchronization with heartbeats (cardiac pulsation) to obtain a reception signal of an ultrasonic echo, the instantaneous position of the object is determined based on the amplitude and phase of the reception signal, and the large amplitude displacement motion of the vascular wall based on the heartbeats is tracked, thereby obtaining the elastic modulus of the blood vessel.
Specifically, a motion velocity waveform of minute vibration of the vascular wall is obtained based on a sequential position of the vascular wall, a tracking trajectory of each of sections given at predetermined intervals in the depth direction in the vascular wall is obtained, and a temporal change in thickness of each section is calculated to obtain the elastic modulus of the blood vessel.
JP 2010-233956 A also describes an ultrasound diagnostic apparatus which obtains an amount of displacement of a blood vessel or the like from a reception signal of an ultrasonic echo obtained by transmitting and receiving ultrasonic waves to and from an object moving in synchronization with heartbeats, and obtains an elastic modulus from the displacement amount.
In this ultrasound diagnostic apparatus, a B-mode image and an M-mode image are produced using a reception signal obtained from an object such as a blood vessel, blurring due to hand or body movement is detected from the reception signal of the M-mode image, a positional variation of the probe and the subject is detected using the reception signal of the M-mode image where the blurring is detected, the accuracy of the reception signal is determined from the detection result, an amount of displacement of the object is obtained using the reception signal of the M-mode image whose accuracy is determined to be high, and the elastic modulus of the vascular wall or the like is measured from the displacement amount.
In order to accurately measure an elastic modulus of a blood vessel or the like based on such a displacement amount of an object moving in synchronization with heartbeats, the analysis needs to be performed particularly with an M-mode image which has a heartbeat suitable for analysis and is less affected by blurring due to hand movement of the tester or body movement of the subject, irregular heartbeats, speckles (speckle noise or speckle pattern) or the like.
Accordingly, for instance, the ultrasound diagnostic apparatus stated in JP 2010-233956 A detects blurring due to hand movement of the tester or body movement of the subject and measures the elastic modulus from the displacement amount of the vascular wall or the like using the reception signal of the heartbeat which is not affected by the blurring due to hand movement and has high accuracy.
Here, in order to measure an accurate elastic modulus of a vascular wall, the analysis needs to be performed using an M-mode image of a complete heartbeat which is fully included from the start through the end (which is fully captured), in addition to being not affected by blurring due to hand movement or the like.